Percussive tools and machines



, Aug. 12, 1969 D.R.JAMES PERCUSSIVE TOOLS AND MACHINES 4 Sheets-Sheet 2 Filed July 5, 1967 ATTORNEYS i 12, 1969 I D. R. JAMES I 3,460, 3

rsncussxvm TOOLS AND MACHINES Filed July 5, 1967 4 Sheets-Sheet 3 Q X) H64. 22-

INVENTOR DAV/p F/c/m/w JAMES m 74 ATTORNEYS.

Aug. 1969 D. R. JAMEs 3,460,636

PERCUSSIVE TOOLS AND MACHINES Filed July 5, 1967 4 Sheets-Sheet 4 INVENTOR fiAW/fi flax/men JAME'S ATTORNEYS United States Patent 3,460,636 PERCUSSIVE TOOLS AND MACHINES David Richard James, Covertside, Hasfield, Gloucester, England, assignor to Sonomotive Engineers Limited, Cheltenham, England Filed July 5, 1967, Ser. No. 651,257 Int. Cl. E21b 1/00; B25d 9/00, N00

US. Cl. 173-116 9 Claims ABSTRACT OF THE DISCLOSURE -A percussive tool or machine derives motive power from a series of fluid pressure pulses produced by a hydraulic generator, and employs a striker into which energy is imparted as a result of the application of the pressure pulses to a piston which may be separate from or formed integrally with the striker. The piston is disposed in a pressure chamber which is connected to the generator, the piston being stepped to provide a differential area on which the fluid pressure acts in the opposite sense to the power stroke. A piston return spring provides the power stroke of the piston.

This invention relates to percussive tools and machines, hereinafter referred to generally as percussive mechanisms and of the type which derive motive power from a series of fluid pressure pulses. The pressure pulses may be produced either by valvular control of a substantially steady supply pressure, or as is preferred by means of an alternating pressure pulse generator to avoid the complications of cyclically operating valve gear. The invention is of particularly advantageous application to tools such as road breaker hammers and rock drills.

Percussive tools and machines of the foregoing type employ a striker into which energy is imparted as a result of the application of the pressure pulses to a piston which may be separate from or formed integrally with the striker. It is customary, and necessary in the case of high-frequency operation, to establish resonant conditions in the tool synchronised closely with the frequency of the pressure pulses; for this purpose the striker is normally mounted so that it reciprocates between a pair of helical or similar springs, it being common practice to apply the pulse energy to the piston in the same sense as the power output stroke. One object of the invention is to provide a percussive tool or machine with which satisfactory resonant conditions can be obtained utilising a single spring.

As a result of applying the pulse energy in the same sense as the output stroke, whilst the kinetic energy in the fluid column applied to the piston on the power stroke becomes additive at the moment of shock impact there is at the same moment a rapid transfer of kinetic to pressure energy in the fluid column, producing the phenomenon commonly referred to as water hammer. This energy transfer is additive to the system pressure which is also reaching, or has reached, a maximum level at this time. The excess total pressure produced places a strain on all the fluid-enclosing system and is particularly detrimental to the flexible hose which usually connects the tool or machine to the power source. Another object of the invention is to provide a percussive tool or machine in which the shock of impact does not result in an excessive pressure rise in the fluid system.

It is one object of the invention to provide a percussive tool or machine having a piston and striker arrangement with the piston disposed in a pressure chamber which in use is connected to a source of fluid pressure pulses, the piston being stepped within the chamber to provide a differential area on which the fluid pressure acts in the op- "ice posite sense to the power stroke, and a piston return spring providing the power stroke of the piston.

'Thus the invention provides an arrangement in which the spring itself provides the power stroke instead of the fluid pressure as in known arrangements, the spring acting as an energy storage device during the application of the pressure pulses to the differential area of the piston. The piston may be formed integrally with the striker, forming an integral member which passes through fluid seals at the opposite ends of the pressure chamber.

The spring may be a helical compression spring or be in the form of a fluid spring utilising a compressible fluid.

According to another object of the invention a percussive tool forming a receiver of a power transmission system of the type, sometimes referred to as an alternating flow or A.F. hydraulic system, in which an hydraulic pulse generator is connected through 'a power line, normally in the form of a single flexible hydraulic hose, to the receiver so that a single hydraulic channel accommodates the alternating flow in both directions, i.e. both towards and away from the receiver. The system may be charged at a predetermined positive make-up pressure, thus providing a datum above atmospheric pressure about which the system pressure alternates. The use of the return spring in accordance with the invention to provide the piston power stroke materially reduces the peak pressure and shock waves which have to be withstood by the flexible hose. Thus the life of the hose is materially increased and the operating conditions with which it has to cope are much :less stringent.

The invention will now be further described with reference to the accompanying drawings which illustrate, by way of example, two forms of road breaker in accordance with the invention. In the drawings:

FIGURE 1 is a diagrammatic sketch which illustrates the functional essentials of the invention,

FIGURE 2 is a side view of one of the road breaker-s, partly in axial section,

FIGURE 3 is an axial section on the line IIIIII in FIGURE 2,

FIGURE 4 is a view similar to that of FIGURE 3 but of the other road breaker, and

[FIGURE 5 is a side view partly shown in section on the line V-V in FIGURE 4.

FIGURE 1 illustrates diagrammatically a percussive tool or motor which in use forms the receiver of an AP. hydraulic power system and which has a generally tubular body 1. An integral piston and striker 2 of cylindrical stepped form is slidable coaxially within the body 1 and has a forward end striking face 3 which strikes a drill bit, or other element to be subjected to the percussive force, during a power stroke of the piston and striker 2.

:Two separate chambers, namely a pressure chamber 4 and a spring chamber 5, are defined within the housing 1 and the pressure chamber 4 has end walls 6 with liquid seals (not shown) through which the piston and striker 2 passes. The piston and striker 2 is stepped at 7 within the pressure chamber 4, which in use is filled with the hydraulic fluid and is connected, through a single flexible hose 3, to the alternating hydraulic power generator 9 of the system.

The step 7 of the piston and striker provides a smaller diameter striker portion 2a which projects through the forward end wall 6 and is formed with said striker face 3, and a larger diameter piston portion 2b which passes through the other end wall 6 and terminates at a spring abutment flange 10 which is engaged by the forward end of a piston return spring '11. Thus the stepped form of the piston and striker is such that hydraulic pulses in the pressure chamber 4 act in the opposite sense to the power stroke, i.e. to retract the piston and striker 2 into the body 1, and during resultant movement of the piston and striker 2 the return spring 11 acts as an energy storage device. On the alternating power strokes the piston and striker 2 is moved solely by the return spring 11, the potential energy stored in the spring being converted to kinetic energy which is capable of doing useful work.

As the system pressure has fallen to a low level at the instance of impact of the striker face 3 there is a complete absence of water hammer effect as in the immediate locality of the differential piston area provided by the stepped formation at 7 there is a sudden depression of pressure below the pulse generator pressure. As a result the system as a whole is protected from the injurious pressure conditions which would otherwise arise with the normal arrangement in which the hydraulic pulses act to provide the power stroke and spring return is employed solely to return the piston in the opposite sense.

Turning now to the practical embodiment of FIG- URES 2 and 3, which where appropriate together with the embodiment of FIGURES 4 and 5 utilises the same reference numerals as the diagram of FIGURE 1, the tubular body -1 is now provided with two diametrically opposed and projecting tubular handles 20 by which the hammer is held when in use. At the forward end the body has a sleeve insert 21 in which a replaceable drill bit 22 of conventional form can be mounted, only a rear end section of the bit being illustrated in the drawings. The bit 22 is detachably retained by a retainer spring 19 mounted on the body 1. The body 1 comprises a forward portion 1a, an intermediate portion 1b and a rear portion in which the handles are mounted. The portions in and 1b are flanged at 23 to enable the portions to be bolted together by rings of bolts 24.

The pressure chamber 4 is formed in the body portion 1b in which is mounted an external hose adaptor 25 for connection of the hose 8. The adjoining ends of the body portions are counterbored to house and locate seal carriers 26 and 27, each of which carries a duplex arrangement of lip-type seals 28 and 29 respectively. The seals 28 define the forward end of the pressure chamber 4 with the seals 29 defining the rear end thereof. A scraper ring 30 mounted on the forward end of the carrier 26 engages the striker portion 2a and provides a seal against contamination of the forward seals 28 by dirt entering the forward end of the body 1. The piston and striker 2 is hollow, having a blind bore 31 drilled from the rear end in order to reduce the inertia to suit the resonant conditions which are required to match the reciprocating system to the frequency of the power generator 9, a typical operating frequency being 30 cycles per second.

Instead of the mechanical spring 11 shown diagrammatically in FIGURE 1 a pneumatic spring is provided. The spring chamber 5 contains air under pressure, this :hamber being closed by an end cap 32 fixed by a ring of bolts 33 to a rear end flange 34 on the body portion la. The chamber 5 is separated from the internal space of the portion 10 by a flexible diaphragm 35 which in FIGURE 3 is shown in the resting or uncharged position and which is clamped around its periphery between the end cap 32 and the flange 34. The internal space of the body portion 10 provides a fluid chamber 36 which in use is charged with the hydraulic operating liquid, and this body of liquid acts as a fluid shield which transmits pressure energy between the pneumatic spring and the piston and striker 2. The spring chamber 5 is pre-charged to the required spring pressure through a check valve 37 mounted centrally in the end cap 32 and protected by a screwed cover 38 which is removed to allow access to the valve.

'A typical operating spring pressure is 100 lbs. per square inch, and this deflects the diaphragm to its precharged position in which it lies flat against an apertured support plate 39 let into the body portion :10 and in effect defining the volume limit of the spring chamber 5. The plate 39 has concentric rings of multiple drillings such as 40 which permit liquid transfer across the plate to and from the fluid chamber 36 and so that the pressure in the latter always acts on the diaphragm 35. Central support for the plate 39 is provided by an apertured cross wall 41 in the body portion 10, which has a central projection to which the plate 39 is riveted.

The outward limit of movement of the piston and striker 2, i.e. movement in the forward power stroke direction, is limited by engagement of the striker face 3 with the rear end of the insert 21 as shown in FIGURE 3. This is the normal resting condition which obtains between periods of use, which periods will normally be somewhat intermittent. Means which will now be described ensure that in the free-running condition the piston and striker 2 does not strike the insert 21 to produce arduous shock load conditions, with attendant noise and risk of mechanical damage. These means are hydraulic in operation and employ a rear end counterbore 42 formed in a bush 43 which is fitted in the body portion 1c and surrounds the piston portion 2b rearwardly of the seal carrier 27. A step 44 at the rear end of the piston portion 2b enters the counterbore 42 as the outer limit of the forward stroke of the piston and striker 2 is approached. Thus some of the hydraulic liquid in the fluid chamber 36 is trapped within the counterbore 42 which in effect provides an arresting chamber, continued forward movement of the piston and striker 2 compressing this liquid to provide a dashpot action. In operation of the hammer this prevents the forward position of the piston and striker 2 being reached, and this is so even when the hammer is free running. The liquid compressed in the counterbore 42 is ejected from latter through a restriction provided by a small annular clearance between the piston portion 2b and the counterbore 42, and in the illustrated construction this clearance is of the order of two thousandths of an inch.

Operation of the hammer is controlled by means of an operating lever 45 which is pivotally mounted on the body portion 10 at 46. The lever 45 overlies one handle 20 and is connected through a link 47 to a piston-valve member 48. The valve member 48 is slidable in a ported sleeve 49 mounted in a bore formed partly in the body portion 1b and partly in the body portion 1c alongside the seal carrier 27. A spring-loaded moving electrical contact 50 is mounted on the forward end of the valve member 48 for cooperation with a fixed electrical contact 52 which is insulated from the body 1. To operate the hammer the lever 45 is gripped to the adjacent handle 20, and this closes the contacts 50 and 52 and moves the valve member 48 against a valve spring 53 to the run position illustrated in FIGURE 2. An electrical lead from the contact 52 nuns back with the hose 8 to the pulse generator 9 for remote control of a hydraulic control valve at the generator. The electrical control circuit employ an earth return utilising metal reinforcing braid of the hose 8.

In the run condition shown in FIGURE 3 ports 54 and 55 in the valve sleeve 49, which respectively communicate with the pressure chamber 4 and the fluid chamber 36, are blanked off so that they do not communicate and hence the chambers 4 and 36 are isolated one from the other during the operation of the hammer. On release of the lever 45 the valve member 48 is returned by the spring 53; as a result the contacts 50 and 52 open to deenergise the control valve at the generator 9 and hence reciprocation of the piston and striker 2 ceases. 'Ilhe valve member 48 moves to a resting position in which a bore 56 in that member interconnects the ports 54 and 55. The hydraulic system includes a make-up pump which tends to maintain a minimum hydraulic pressure of say lbs. per square inch, and maintains this pressure when the generator 9 is inoperative as a result of the contacts 50 and 52 being open. This condition corresponds to a valve position in which the chambers 4 and 36 intercommunicate, and this ensures that when the hammer is idle the chamber 36 is pre-charged to the make-up pressure ready for operation. The make-up pressure is also applied to the rear end of the piston and striker 2, with resultant forward movement of the piston and striker to the forward limit position (illustrated in FIGURE 3) against the opposition of the saline hydraulic pressure acting on the relatively small step 7. Thus movement of the valve member 48 to the idle position not only ensures that the chamber 36 is pre-charged to the correct pressure but also that it contains the correct volume of hydraulic liquid, i.e. the volume corresponding to the forward limit defined by abutment of the piston and striker 2 with the insert 21.

Thus the automatic operation of the valve 48 assists in maintaining steady and optimum running conditions, immediately after use the liquid in the chamber 36 being correctly adjusted as regards both pressure and volume. During operation there is a tendency :for pressure in this chamber to increase, as a result not only of increasing temperature but also of any leakage from the pressure chamber 4 past the seals 29. During setting up of the hammer with the make-up pump running the valve 48 operates to pre-charge the chamber 36, any air being displaced past a bleed screw 57 which is slackened ofi? for the purpose. With the correct pressure condition in the chamber 36 the chamber 5 can be pre-charged with compressed air to the correct spring pressure, and the hammer is then ready for use by operation of the lever 45.

The use of the fluid shield provided by the hydraulic liquid in the chamber 36, together with the flexible diaphragm 35, provides a particularly convenient manner of utilising a pneumatic spring as there are no problems of air leakage from the spring or contamination by leakage from the pressure chamber 4 and yet the spring force is applied satisfactorily and directly to the piston and striker 2. The liquid in the chamber 36 in eifect acts as a liquid connecting rod, and what can be termed a hydro-pneumatic spring system results. As an example of typical operating conditions in the embodiment of FIGURES 2 and 3, with the spring pre-charged to a pressure of 100 lbs. per square inch a maximum spring pressure of 380 lbs. per square inch results with a hydraulic operating pressure the pulses of which produce pressure variations between 60 and 1,800 lbs. per square inch at an operating frequency of 30 cycles per second.

The embodiment of FIGURES 4 and 5 is fundamentally similar to that of FIGURES 2 and 3 but is somewhat simpler and has one important modification. The modification is that the spring chamber 5, again defined between an end cap 32 and a flexible diaphragm 35, is angled over to one side as shown more particularly in FIGURE 5. This produces a shorter and more compact tool, in which the handles 20 and the operating lever 45 can be disposed at the rear end of the body 1, which allows more convenient and comfortable operation particularly as the operator is well clear of the end plate 32 which during prolonged operation of the hammer may tend to become rather hot to the touch. The embodiment is simpler in that the body 1 now comprises only two portions, a forward portion 1a and a rear portion 1b. A sleeve 60 which fits a counterbore in the forward end of the body portion 1b acts as a carrier for the lip-type seals 28 and 29, in this case only one such seal being employed at each end of the pressure chamber 4. The use of the liquid in the chamber 36 to transfer the spring force to the piston and striker 2 now has the additional advantage that the angled position of the spring chamber 5 in no way affects the efliciency of operation.

In FIGURES 4 and 5 the 'apertured plate 39 is not let into the body 1, but is sandwiched between the body portion 1b and the end cap 32. This simplifies machining, and the plate 39 is fixed entirely by the cap securing bolts 33.

I claim:

I. An alternating flow hydraulic power transmission system comprising a power source to produce a continuous series of fluid pressure pulses, a percussive mechanism, and a power line which accommodates the alternating hydraulic flow in both directions to and 'from the receiver, the percussive mechanism having a piston and striker arrangement with the piston accessible to the fiuid pressure pulses within a pressure chamber to which the power line is connected and in which the fiuid pressure acts on the piston in the opposite sense to a power stroke of the mechanism, and a piston return spring which provides the power stroke of the piston.

2. A percussive mechanism comprising an alternating flow hydraulic pulse generator, a piston and striker, a pressure chamber in which said piston is disposed, a single flexible hose connecting said pulse generator to said chamber to accommodate the alternating hydraulic flow in both directions to and from the chamber, said piston being stepped within said chamber to provide a difierential area on which the pressure pulses act in the opposite sense to a power stroke of the piston, and piston return spring means acting on the piston to provide said power stroke of the piston.

3. A percussive mechanism as claimed in claim 2, said piston and striker forming an integral member, and fiuicl seals at opposite ends of the pressure chamber through which said integral member passes in fluid-sealed relationship.

4. A percussive mechanism as claimed in claim 1, said piston return spring means being pneumatic.

5. A percussive mechanism as claimed in claim 4, said pneumatic spring means comprising a chamber, means for precharging said chamber to a desired spring pressure, and a flexible diaphragm that bounds one side of said pneumatic spring means and by which the reaction of said pneumatic spring means is applied.

6. A percussive mechanism as claimed in claim 5, and an apertured plate into contact with which said diaphragm is movable to limit the size of said pneumatic spring chamber.

7. A percussive mechanism as claimed in claim 5, the fluid in said pressure chamber being a hydraulic operating liquid, there being a confined body of said liquid between the return spring means and the piston, and means responsive to a condition of the percussive mechanism in which the piston is not delivering power strokes, for placing said pressure chamber and said body of liquid in communication with each other.

8. A percussive mechanism as claimed in claim 7, the piston within the pressure chamber being stepped, the area of the piston perpendicular to the axis of the piston and exposed to said body of liquid being greater than the stepped area of the piston within said pressure chamber, so that when the piston is not delivering power strokes,

the application of pressure to said body of liquid moves UNITED STATES PATENTS 3/1946 Mannerstedt et a1. 173-1 19 7/1967 Klebanov 173134 JAMES A. LEPPINK, Primary Examiner U.S. Cl. X.R. 

